This invention relates to color video cameras, and in particular to those employed in confined spaces, such as in borescopes or endoscopes of the type in which a miniature video camera is mounted at a distal viewing head of an elongated insertion tube. The invention is more specifically concerned with an arrangement of the miniature video camera which produces color video images using a single monochrome video imaging device combined with a controllable color filter assembly.
Recently, interest has increased in the use of video instruments for surgical applications to permit a surgeon to carry out a procedure with minimal intervention in the patient. An example of one such video instrument is a laparoscope for performing surgery in the abdominal cavity, where the instrument is inserted through a small incision. There is also an increased interest in remote imaging of industrial processes, such as inspection of heat exchanger tubes or of turbine engines, where remote color imaging could be employed to advantage.
However, in current imaging systems, either a complex and expensive color imaging CCD type device is employed or else color sequential illumination is provided to produce red, blue, and green illumination in turn onto the target of the camera or imaging assembly.
Full-color video borescopes and endoscopes are well known, and have been described, for example, in Danna et al. U.S. Pat. No. 4,491,365, Danna et al. U.S. Pat. No. 4,539,586, and Longacre et al. U.S. Pat. No. 4,523,224. The latter describes a colorsequential system in which sequential primary color light is supplied over a fiber optic bundle to illuminate the target area sequentially with primary color light. With the present systems a white illumination source is sequentially pulsed to produce red, green and blue light that is then carried over a fiber optic bundle to the probe tip. The illumination is pulsed mechanically using a chopper wheel or filter wheel which must be synchronized with the display electronics. This filter wheel is big, slow to synchronize, mechanically complex and expensive. The systems of this type require a built-in light source and cannot be made to produce a color image with ambient light.